Former FBI director James Comey has said Donald Trump is a man "morally unfit to be president", who treats women like "pieces of meat".
Mr Comey was giving his first major television interview since he was was fired by President Trump last year.
He told ABC News that Mr Trump lies constantly and may have obstructed justice.
Hours before the interview aired, the president went on the offensive, accusing Mr Comey of "many lies".
"I don't buy this stuff about him being mentally incompetent or early stages of dementia," Mr Comey told ABC's 20/20 programme on Sunday night.
"The only thing worse than Comey's history of misconduct is his willingness to say anything to sell books," it said.
How did we get here?
It is the latest development in a long-standing feud between the two men, further fuelled by the upcoming publication of Mr Comey's memoir A Higher Loyalty: Truth, Lies and Leadership.
The ex-FBI chief is on a publicity blitz for the book.
President Trump has said the" badly reviewed book" raises "big questions". He also suggested Mr Comey should be imprisoned, and in recent days began referring to him as a "slimeball".
The story dates back to the 2016 presidential election, when Mr Comey was FBI director. In October, days before the vote, he sent a letter to Congress telling them the FBI was reopening an investigation into Hillary Clinton's emails. The letter went public - and Mrs Clinton says it handed Donald Trump the election.
But once Mr Trump became president, Mr Comey says he tried to extract a pledge of personal loyalty from him - something the president fiercely denies.
In March 2017, when alleged links between Mr Trump's campaign and Russia were being investigated by the FBI, Mr Trump allegedly pressured Mr Comey to publicly declare that the president was not personally being investigated - something the then director says he declined to do.
Some Democrats blamed Mr Comey for costing Mrs Clinton the election, while Trump supporters felt he was targeting the president with the Russia investigation.
He was fired by President Trump in May, finding out about his dismissal from TV news.
Getting out alive?
James Comey thinks Donald Trump is a serial liar who degrades women and is "morally unfit" to be president.
He says it's "possible" but "unlikely" that Russia has compromised the president, and that he may have obstructed the collusion investigation.
He also believes the American people can't do anything about it until the November 2020 presidential election.
That's just one of the contradictions that emerged in Mr Comey's interview. He said he strove to make non-political decisions about the highly political 2016 investigations into Hillary Clinton and the Trump campaign. He spoke of integrity and honour, but confessed that he may not have had the "guts" to confront the president.
The former director gave a complex interview reflecting a man challenged to draw meaning from his place at the centre of the biggest political stories of a lifetime. It made for gripping television. Now Trump loyalists will pick apart his remarks and return fire.
"Nobody gets out alive," Mr Comey quipped in the early days of the Clinton investigation.
It wasn't really a joke then. And it certainly isn't now.
What else did Comey say?
ABC News released a full 42,000-word transcript of the interview between Mr Comey and chief anchor George Stephanopoulos.
In the primetime TV interview, Mr Comey suggested that the president had surrounded himself with people loyal to him - comparing Mr Trump to mob bosses he had investigated as a younger man.
"The loyalty oaths, the boss as the dominant centre of everything, it's all about how do you serve the boss, what's in the boss' interests," he said.
Asked if those around the president were "enabling bad behaviour", Mr Comey said: "The challenge of this president is that he will stain everyone around him."
Mr Comey, however, said he did not believe President Trump should be impeached.
"I hope not because I think impeaching and removing Donald Trump from office would let the American people off the hook," he said.
Instead, he said, it was something the American people were "duty bound to do directly" at the voting booth.
During the extensive interview, Mr Comey also said:
- Before revealing the new Clinton investigation, one staff member asked Mr Comey: "Should you consider that what you're about do to may help elect Donald Trump president?"
- To which Mr Comey said he responded: "Down that path lies the death of the FBI as an independent force"
- On the Clinton probe: "The FBI drove this investigation and we did it in a competent and independent way. I would bet my life on that"
- He was a "deeply flawed human surrounded by other flawed humans"
- Readers of his book "may still walk out of this thinking I'm an idiot, but I'm an honest idiot"
